Bauerle, S. F.; Reetz, L. S.; Denzinger, A.

Acoustic communication plays a central role in animal social behavior and exhibits remarkable complexity in various taxa. In bats, the emission of echolocation calls is tightly coupled to wingbeat and respiratory rhythms. However, little is known about how complex social vocalizations are coordinated with the mechanics for powered flight. We investigated how complex social calls are integrated into flight of wild Nathusius' pipistrelles (Pipistrellus nathusii). Using synchronized audio and video recordings, we quantified wingbeat rhythms during free flight and incorporated these data into a kinematic inference model to reconstruct the timing of social calls relative to the wingbeat. We found that echolocation call emission is coupled to the upstroke phase of the wingbeat. Moreover, social calls span three wingbeat cycles during flight and are embedded within a continuous sequence of echolocation calls. While motif durations scale with syllable number, motif onsets are phase-locked to narrow, preferential phases of the wingbeat cycle. Our findings provide evidence that complex social calls in bats are integrated into the wingbeat during flight, demonstrating that vocal-locomotor coupling extends beyond echolocation to shape the structure of social communication. By mitigating the high energetic costs of vocalizing, biomechanical integration might have facilitated the evolution of complex vocal communication in bats.